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Abstract:

A dual fuel boiler has a granular fuel burner and a fluid fuel burner.
The fluid fuel burner is movable between a retracted stored position at a
side of a combustion chamber-of the boiler and an extended operative
position in which it extends out over a brazier of the granular fuel
burner. Thus in the operative position substantially all of the flame and
hot combustion gases generated by the fluid fuel burner in use are
directed away from the brazier to prevent damage to the brazier.

Claims:

1. A boiler dual fuel burner assembly comprising a granular fuel burner
and a fluid fuel burner and an air supply duct and associated fan for
feeding the granular fuel burner and associated granular fuel brazier and
the fluid fuel burner characterised in that the fluid fuel burner is
movable into an operative position within the combustion chamber in which
substantially all of the flame and combustion gases generated by the
fluid fuel burner in use are directed away from the brazier.

2. The dual fuel burner assembly as claimed in claim 1 wherein the fluid
fuel burner is movable between a retracted stored position and an
extended operative position.

3. The dual fuel burner assembly as claimed in claim 2 wherein the fluid
fuel burner locates at a side of the combustion chamber when in the
stored position.

4. The dual fuel burner assembly as claimed in claim 2 wherein the fluid
fuel burner locates outside the combustion chamber when in the stored
position.

5. The dual fuel burner assembly as claimed in claim 1 wherein the fluid
fuel burner projects into the combustion chamber when in the operative
position.

6. The dual fuel burner assembly as claimed in claim 1 wherein the fluid
fuel burner extends out over the brazier when in the operative position.

7. The dual fuel burner assembly as claimed in claim 2 wherein the fluid
fuel burner is slidably movable between the stored position and the
operative position.

8. The duel fuel burner assembly as claimed in claim 2 wherein an
actuator is connected to the fluid fuel burner, said actuator being
operable for moving the fluid fuel burner between the stored position and
the operative position.

9. The duel fuel burner assembly as claimed in claim 8 wherein the
actuator comprises a rack attached to the fluid fuel burner and an
associated drive pinion which operably engages the rack and a drive motor
driveably connected to the pinion.

10. The dual fuel burner assembly as claimed in claim 2 wherein the fluid
fuel burner is mounted on a telescopic support for movement between the
stored position and the operative position.

11. The dual fuel burner assembly as claimed in claim 10 wherein the
telescopic support comprises a blast tube slidably mounted within an
outer support tube, the blast tube being movable through said outer
support tube by means of the actuator which is connected to the blast
tube, a fluid fuel burner nozzle being mounted at an outer end of the
blast tube.

12. The dual fuel burner assembly as claimed in claim 11 wherein the
blast tube forms an air duct for delivery of combustion air to the
nozzle.

13. The dual fuel burner assembly as claimed in claim 12 wherein the
blast tube has at least one air inlet opening which communicates with the
air supply duct when the blast tube is in an extended operative position
corresponding to the operative position of the burner.

14. The dual fuel burner assembly as claimed in claim 1 wherein the air
duct has an outlet communicating with the brazier, a valve mounted at the
outlet and being operable to close the outlet when the fluid fuel burner
is in the operative position.

15. The dual fuel burner assembly as claimed in claim 14 wherein the
valve is biased into an open position and is movable against said bias
into a closed position by means of a ram.

16. The dual fuel burner assembly as claimed in claim 15 wherein the ram
is operably connected to the fluid fuel supply for the fluid fuel burner
such that pressurisation of the fluid fuel for delivery to the fluid fuel
burner operates the ram to close the valve.

17. The dual fuel burner assembly as claimed in claim 14 wherein the
valve is mounted on the blast tube such that the valve is closed when the
blast tube is in the extended operative position and the valve is open
when the blast tube is in the refracted position.

Description:

[0002] The invention particularly relates to a boiler dual fuel burner
assembly of the type comprising a granular fuel burner, a fluid fuel
burner and an air supply duct and associated fan for feeding a granular
fuel burner and associated granular fuel brazier and the fluid fuel
burner. Such boilers are generally enclosed water heating boilers
comprising walls forming a combustion chamber enclosure, hollow heat
exchangers arranged for carrying water to be heated, usually provided by
at least portion of the walls of the combustion chamber which are hollow
water-containing walls. Generally, there is a granular fuel burner and
associated granular fuel brazier. The burner is usually some form of
electrode but many other types of burner may be used. Generally, they are
used to heat the air which then causes the granular fuel to ignite. The
fluid fuel burner is, for example, a conventional gas or oil fired
burner.

[0003] In this specification, the term "granular fuel" is used to include
not only granular fuel such as wood pellet formed from wood sawdust, but
also other solid materials such as ground or semi-shredded husks of maize
and similar products, together with particles of combustible waste
material and other recognised fuels such as coal, peat and similar
materials.

[0004] As stated above, in many such boiler constructions, the granular
fuel is contained on a brazier and an electric element is used to heat
the granular fuel. The granular fuel in these boilers is very often wood
pellets. After a certain amount of time, the wood, or other granular
fuel, spontaneously ignites.

[0005] Problems do arise with the braziers, for example, there is
described a unique construction of brazier in our co-pending European
Patent Application No. 08169363.2, filed on Nov. 18, 2008, the disclosure
of which is incorporated herein by direct reference. There are, however,
certain problems with granular fuel, if only the problem of the need to
have a sufficient supply of the fuel. Unfortunately, sometimes the fuel
gets damaged due to moisture, when it very often becomes unusable,
particularly if the granular fuel being used is wood pellets which are
essentially compressed sawdust, without any binder, such that when they
get wet, they become useless. There is therefore a need for a standby
burner assembly for the boiler, which standby burner assembly is fluid
fired, whether liquid or gaseous.

[0006] Unfortunately, there are problems in providing these standby burner
assemblies. Where the fluid fired boiler is mounted at the entrance to
the boiler, side-by-side with the brazier the temperature of ignition of
the fluid fired burner is such that the brazier tends to get damaged by
the hot flame and combustion gases. While obviously one could avoid this
problem by mounting the two burners far apart, this is essentially
impractical in most constructions of boiler and further, as well as being
impractical, causes considerable mounting problems.

[0007] It is known to provide dual fuel burner assemblies for boilers
comprising a granular fuel burner and a fluid fuel burner, usually an oil
fired burner, however, these are used more to provide ignition for the
granular fuel than as purely a stand-by fuel assembly. For example, in
PCT Publication No. WO 2008\068587 (Ecoflam Bruciatori S.P.A.) there is
described such a dual fuel boiler where the fluid fired burner is used to
ignite the granular fuel. It is also known to have a similar construction
to that of the afore referenced boiler for backup. However, the problem
with these dual fuel burner assemblies is that, for example, with an oil
burner, the combustion gases are of the order of 1100° C. and
1200° C., which is extremely hot. This unfortunately causes damage
to the surrounding metal and particularly to the brazier. Essentially,
then the braziers are destroyed if such an assembly is used for providing
back-up heat when granular fuel is unavailable.

[0008] The present invention is directed towards providing a boiler dual
fuel burner which overcomes these problems and which will be such as to
be easily fitted into a boiler shell and not one that will cause damage
to, for example, the brazier used in the combustion of the granular fuel.

SUMMARY OF THE INVENTION

[0009] The present invention is characterised in that the fluid fuel
burner is movable into an operative position within the combustion
chamber in which substantially all of the flame and combustion gases
generated by the fluid fuel burner in use are directed away from the
brazier. Thus advantageously the brazier is protected and is not damaged
by operation of the fluid fuel burner.

[0010] In one embodiment of the invention the fluid fuel burner is movable
between a retracted stored position and an extended operative position.

[0011] In another embodiment of the invention the fluid fuel burner
locates at a side of the combustion chamber when in the stored position.

[0012] In another embodiment of the invention the fluid fuel burner
locates outside the combustion chamber when in the stored position.

[0013] In a further embodiment of the invention the fluid fuel burner
projects into the combustion chamber when in the operative position.

[0014] In another embodiment of the invention the fluid fuel burner
extends out over the brazier when in the operative position.

[0015] In another embodiment of the invention the fluid fuel burner is
slidably movable between the stored position and the operative position.

[0016] In another embodiment of the invention an actuator is connected to
the fluid fuel burner, said actuator being operable for moving the fluid
fuel burner between the stored position and the operative position.

[0017] Conveniently the actuator comprises a rack attached to the fluid
fuel burner and an associated drive pinion which operably engages the
rack and a drive motor driveably connected to the pinion.

[0018] In another embodiment of the invention the fluid fuel burner is
mounted on a telescopic support for movement between the stored position
and the operative position.

[0019] In another embodiment of the invention the telescopic support
comprises a blast tube slidably mounted within an outer support tube, the
blast tube being movable through said outer support tube by means of the
actuator which is connected to the blast tube, a fluid fuel burner nozzle
being mounted at an outer end of the blast tube.

[0020] In another embodiment of the invention the blast tube forms an air
duct for delivery of combustion air to the nozzle.

[0021] In another embodiment of the invention the blast tube has at least
one air inlet opening which communicates with the air supply duct when
the blast tube is in an extended operative position corresponding to the
operative position of the burner.

[0022] In another embodiment of the invention air duct has an outlet
communicating with the brazier, a valve mounted at the outlet and being
operable to close the outlet when the fluid fuel burner is in the
operative position.

[0023] In another embodiment of the invention the valve is biased into an
open position and is movable against said bias into a closed position by
means of a ram.

[0024] In another embodiment of the invention the ram is operably
connected to the fluid fuel supply for the fluid fuel burner such that
pressurisation of the fluid fuel for delivery to the fluid fuel burner
operates the ram to close the valve.

[0025] In another embodiment the valve is mounted on the blast tube such
that the valve is closed when the blast tube is in the extended operative
position and the valve is open when the blast tube is in the retracted
position.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The invention will be more clearly understood from the following
description of some embodiments thereof, given by way of example only,
with reference to the accompanying drawings, in which:

[0027] FIG. 1 is a side diagrammatic view of a boiler incorporating a dual
fuel burner assembly according to the invention, in a position in which
granular fuel is being burned;

[0028] FIG. 2 is a view similar to FIG. 1, in which a fluid fuel burner is
being used;

[0029] FIG. 3 is a view similar to FIG. 1 showing another boiler according
to a second embodiment of the invention; and

[0030] FIG. 4 is a view similar to FIG. 2 of the boiler of FIG. 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0031] Referring to the drawings, and initially to FIGS. 1 and 2 thereof
there is provided a dual fuel boiler, indicated generally by the
reference numeral 1, comprising a base 2 and upstanding side walls 3. The
boiler 1 is divided into a combustion chamber 4 and a heat transfer and
condensing unit 5, containing conventional boiler tubes and, for example,
including water-filled walls. Mounted on the base 2 is an ash pan 6. All
of this is conventional.

[0032] There is further provided a dual fuel burner assembly, indicated
generally by the reference numeral 10, comprising a granular fuel burner
indicated generally by the reference numeral 11, and a fluid fuel burner,
indicated generally by the reference numeral 12, and more clearly
illustrated in FIG. 2. The whole of the granular fuel burner 11 is not,
strictly speaking illustrated fully as the electrodes are mounted behind
the fluid fuel burner 12 in an air chamber which will be described
hereinafter.

[0033] A wood pellet supply duct 20 feeds an air chamber 21 which in turn
is fed by a fan 22. The air chamber 21 is connected to a brazier 23
through an outlet 24 having an associated valve 24a. The side valve 24a
is connected by a con rod 25 and return spring 26 to a hydraulic ram 27
fed by oil through an oil line 28 from a combined motor and oil pump 29.
The construction of brazier 23 is described in more detail in our
co-pending European Patent Application No. 08169363.2 previously
referenced.

[0034] The fluid fuel burner, in this embodiment an oil burner 12,
comprises an injector nozzle 30 mounted in a blast tube 31. The blast
tube 31 includes air supply openings 32 and is in turn mounted in a
support tube 33. The support tube 33 further houses a rack 34 and pinion
35 driven by a motor 36. A flexible oil supply line 37 feeds, from the
combined motor and oil pump 29, fuel to the injector nozzle 30. The motor
36 is operable to drive the pinion 35 which in turn drives the rack 34
for sliding the blast tube 31 within the support tube 33. Thus, the fluid
fuel burner 12 can be moved between a retracted stored position as shown
in FIG. 1 and an extended operative position as shown in FIG. 2. As can
be seen in the drawings, when in the retracted stored position, the fluid
fuel burner 12 locates at a side of the combustion chamber 4 outside the
combustion chamber 4 and when in the extended operative position, the
fluid fuel burner 12 projects into the combustion chamber 4, extending
out over the brazier 23. The rack 34, pinion 35 and motor 36 together
form an actuator for slidably moving the fluid fuel burner 12 between the
stored position and the operative position.

[0035] The blast tube 31 and associated support tube 33 together form a
telescopic support for the fluid fuel burner 12. It will be noted that
when the blast tube 31 is in the extended position as shown in FIG. 2 a
number of circumferentially spaced-apart air supply openings 32 in a side
wall of the blast tube 31 communicate with the air chamber 21 for supply
of combustion air through the blast tube 31 to the injector nozzle 30.
Similar openings may be provided in the support tube 33 for
through-passage of air, or alternatively the air supply openings 32 may
be positioned outwardly of an outer end of the support tube 33 when the
blast tube 31 is in the fully extended position.

[0036] As the oil pump 29 is switched on to supply pressurised fuel to the
injector nozzle 30, pressurised oil is delivered through the oil line 28
to the ram 27 which overcomes spring 26 bias to close the valve 24a
cutting off air supply to the brazier 23.

[0037] Finally, it will be noted that above the brazier 23, there is
mounted a canopy 40, which canopy 40 is to make sure the combustion in
the brazier 23 is full combustion and that there is not residual carbon
monoxide (CO) in the boiler to be subsequently exhausted to atmosphere.

[0038] In operation, and referring firstly to FIG. 1 where the boiler 1 is
shown in operation as a wood pelletted boiler, namely, with the granular
fuel burner 11 in operation, wood pellets are delivered through the wood
pellet supply duct 20 into the brazier 23 in conventional manner.
Simultaneously, air is delivered by the fan 22 into the air chamber 21
and through the outlet 24, the valve 24a of which is now open, and into
the brazier 23 for normal combustion. The air in the air chamber 21
bypasses the support tube 33 and blast tube 31.

[0039] In operation, when it is desired to use the fluid fuel burner, in
this case, the oil burner 12, the motor 36 is operated and the blast tube
31 is extended from a retracted stored position within the support tube
33. The air supply openings 32 in the blast tube 31 are exposed and air
is delivered from the air chamber 21 through the blast tube 31 to the
burner 12 injector nozzle 30. The valve 24a is shut by the hydraulic ram
27 closing the outlet 24 to the brazier 23.

[0040] It will be noted that now the combustion flame and gases generated
by the injector nozzle 30 are injected into the combustion chamber 4
remote from the brazier 23 and are directed away from the brazier 23.

[0041] Referring now to FIGS. 3 and 4, there is illustrated another duel
fuel boiler indicated generally by the reference numeral 50. It is
largely similar to the boiler 1 described previously and like parts are
assigned the same reference numerals. In this case the valve 24a is
mounted by an arm 52 on the blast tube 31 such that the valve 24a is
closed when the blast tube 31 is in the extended operative position shown
in FIG. 4 and the valve 24a is open when the blast tube 31 is in the
retracted position shown in FIG. 3. A suitable opening is provided in the
support tube 33 for through-passage of the arm 52. Other than this the
construction and operation of the boiler 50 is similar to that for the
boiler 1 described previously.

[0042] In this specification, the terms "comprise", "comprises",
"comprised" and "comprising" and the terms "include", "includes",
"included" and "including" are deemed totally interchangeable and should
be afforded the widest possible interpretation.

[0043] The invention is in not limited to the embodiments hereinbefore
described but may be varied in both construction and detail, within the
scope of the appended claims.